In eye surgery, the illumination in an ophthalmic surgical microscope must often meet special requirements. For example, in cataract surgery, illumination systems are used which illuminate the patient's eye in such a way that the illumination beam path extends substantially coaxially with the observation beam path of the surgical microscope. This produces the so-called red reflex, in which the light scattered back from the retina causes the pupil of the patient's eye being operated on to shine with a reddish light. This red reflex illumination is advantageous, particularly in cataract surgery, because residual tissue, which may be left after the removal of the eye lens from the lens capsule and has to be removed to avoid complications, can be detected particularly easily against the backlight provided by the red reflex.
The red reflex seen by the operator is highly dependent on the individual characteristics of the patient's eye to be operated on. Experience shows that a patient's eye which is myopic and therefore relatively long provides a poorer red reflex than an eye which is hyperopic and therefore shorter. It is therefore advantageous if the illumination can be adapted to the individual characteristics of the patient's eye being operated on.
German Publication DE 92 17 517 U1 describes a surgical microscope having an illumination system which allows red reflex illumination of the lens capsule. In order to increase the contrast according to any possible ametropia of the patient, a lens, which was selected prior to surgery to match the ametropia of the eye, is swung in between the microscope objective and the patient's eye. However, this approach is relatively complex.
In German Patent Application DE 40 28 605 A1, an illumination system for an ophthalmic surgical microscope is described which includes a light source for emitting light along an illumination beam path directed toward an eye of a patient, as well as two deflection mirrors, each of which directs part of the illuminating light to the surgical area. One of the two deflection mirrors is adjustable to vary the angle at which the illuminating light deflected by it strikes the surgical area.
German Patent Application DE 10 2005 042 436 A1 describes an illumination system for an ophthalmic surgical microscope, including a light source for emitting light toward an eye of a patient, and a measuring device for measuring a parameter of the patient's eye. A model of the patient's eye is calculated based on the measured parameter. This model of the patient's eye is then displayed on a display device.
German Patent Application DE 102 02 509 A1 discloses an ophthalmic surgical microscope of the kind set forth in the preamble of claim 1, which uses a refractometer allowing parameters of the patient's eye being operated on to be determined in situ; i.e., during surgery. This enables the operator to take corrective measures during surgery, for example to minimize any detected residual ametropia.